The present invention relates to an electron beam exposure apparatus, reduction projection system, and device manufacturing method and, more particularly, to an electron beam exposure apparatus for drawing a pattern on a sample by an electron beam, a reduction projection system suitable for the electron beam exposure apparatus, and a device manufacturing method using the electron beam exposure apparatus.
An electron beam exposure apparatus can form a fine circuit pattern but has not been introduced into the semiconductor manufacturing process so far. This is because its throughput is lower than that of an optical exposure method. In recent years, various techniques have been developed to remove this drawback. One of these methods is a transfer exposure method of exposing a large exposure area at once by using a transfer mask. A projection lens adopted in an apparatus of this type is a symmetrical doublet type magnetic lens.
The use of the symmetrical magnetic doublet allows correcting all anisotropic aberrations among third-order aberrations, chromatic aberration concerning rotation and magnification, and isotropic distortion (M. B. Heritage, J. Vac. Sci. and Technol., Vol. 12, No. 6, November/December, 1975).
Even in the use of the symmetrical magnetic doublet, the aberration amount increases for a large converging angle (aperture) of an electron beam. Along with this, the resolution decreases, failing to constitute a practical electron beam exposure apparatus. For example, to obtain an allowable aberration amount necessary to attain a resolution of 100 nm or less, the electron beam converging angle must be set to 2 to 3 mrad. At such a converging angle, the image greatly blurs due to the coulomb interaction. To avoid this, the electron beam irradiation amount, i.e., current must be decreased, which limits the throughput.
An immersion lens method of forming a lens magnetic field for converging an electron beam on an image plane of a projection lens can attain small-axial aberration conditions even at a large converging angle (aperture), compared to a method of not forming any lens magnetic field on the image plane.
If immersion lenses are employed as the image plane side electron lens of a projection lens made up of two electron lenses, the symmetry between front and rear lenses cannot be obtained, unlike the symmetrical magnetic doublet. It is difficult to cancel image distortion between the front and rear lenses, generating a large image distortion.
The present invention has been made in consideration of the above situation, and has as its object to reduce any blur and image distortion of an electron beam on a sample even at a large converging angle of the electron beam.
According to the first aspect of the present invention, there is provided an electron beam exposure apparatus comprising a reduction projection optical system having an immersion lens, a table which holds an object to be exposed, and a pupil control optical system which forms an entrance pupil at a finite position on a downstream side of an image plane, wherein the reduction projection optical system and the pupil control system project a pattern onto the object.
According to the preferred embodiment of the present invention, the pupil control optical system preferably forms the entrance pupil at a position where both a blur and image distortion of the electron beam on the object are reduced.
According to the further preferred embodiment of the present invention, the pupil control optical system forms the entrance pupil at a position where both a blur and image distortion of the electron beam on the object are substantially minimized.
According to the preferred embodiment of the present invention, the pupil control optical system includes a field lens.
According to the preferred embodiment of the present invention, the pupil control optical system is arranged between the reduction projection optical system and the object plane.
According to the preferred embodiment of the present invention, the reduction projection optical system is formed from two electron lenses, and one of the electron lenses includes the immersion lens.
According to the second aspect of the present invention, there is provided an electron beam exposure apparatus comprising a reduction projection optical system having an immersion lens, a table which holds an object to be exposed, and a field lens, wherein the reduction projection optical system and the field lens project a pattern onto the object.
According to the preferred embodiment of the present invention, the reduction projection optical system is preferably formed from two electron lenses, and one of the electron lenses includes the immersion lens.
According to the third aspect of the present invention, there is provided a reduction projection system for reducing and projecting an image formed by an electron beam, comprising a reduction projection optical system having an immersion lens, and a pupil control optical system which forms an entrance pupil of the reduction projection system at a finite position on a downstream side of the image plane of the reduction projection system.
According to the fourth aspect of the present invention, there is provided a reduction projection system for reducing and projecting an image formed by an electron beam, comprising a reduction projection optical system having an immersion lens, and a field lens arranged on an object side of said reduction projection optical system.
According to the fifth aspect of the present invention, there is provided a device manufacturing method comprising the steps of applying a photosensitive agent to a substrate, drawing a pattern on the substrate by an electron beam exposure apparatus, and developing the substrate, wherein the electron beam exposure apparatus has a reduction projection optical system having an immersion lens, a table which holds the substrate, and a pupil control optical system which forms an entrance pupil at a finite position on a downstream side of an image plane, wherein the reduction projection optical system and the pupil control system project a pattern onto the substrate.
According to the sixth aspect of the present invention, there is provided a projection system comprising a plurality of electron lenses including an immersion lens, wherein an electron incidence side of the plurality of electron lenses is not telecentric.
According to the seventh aspect of the present invention, there is provided an exposure apparatus comprising a stage for holding an object to be exposed, and a plurality of electron lenses, including an immersion lens, for projecting an electron beam onto the object, wherein said plurality of electron lenses are not telecentric on an electron incidence side thereof.
According to the preferred embodiment of the present invention, the exposure apparatus further comprises a stage for holding a mask, and an illuminator for illuminating the mask with the electron beam, wherein a plurality of electron lenses project the electron beam from the mask onto a wafer as the object to be exposed.
According to the eighth aspect of the present invention, there is provided a device manufacturing method comprising the steps of exposing a substrate by using an exposure apparatus, and developing the exposed substrate, wherein the exposure apparatus comprises s stage for holding the substrate and a plurality of electron lenses, including an immersion lens, for projecting an electron beam onto the substrate, wherein said plurality of electron lenses are not telecentric on an electron incidence side thereof.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.